The dark red chocolate cosmos flowers balance atop thin wiry stems.
The pretty cosmos flower that is such a familiar summertime bedding plant (Cosmos bipinnatus) is an annual; so is the less well known but just as pretty, orange cosmos (C. sulphureus). Chocolate cosmos, on the other hand, is a perennial: an herbaceous perennial that dies to the ground in winter and returns the following spring. This is a multi-stemmed plant that grows 16-30 in (40-75 cm) tall and up to 24 in (60 cm) across from underground tubers. Chocolate cosmos has reddish brown stems with compound (pinnate) leaves 3-6 in (7-15 cm) long. The leaves are divided into diamond shaped leaflets, and some of them are divided again (twice compound or bipinnate). The flowers aren’t really black, but the 6-10 (usually 8) velvety rays are a deep, dark maroon or oxblood color and the disks an even darker brown. The flowerheads, about an inch to an inch and three quarters (2.5-4.4 cm) across, are carried on thin wiry stems well above the foliage. They have a distinctive chocolaty smell which goes well with the color!
Chocolate cosmos (Cosmos atrosanguineus) came originally from Mexico. It is now assumed to be extinct in the wild, surviving only in cultivation as a single clone first introduced in 1902.
Chocolate cosmos does well in poor, sandy soils. Light: Grow chocolate cosmos in full sun. Moisture: Water regularly the first year in the ground. After that your chocolate cosmos should be able to withstand most dry spells. Chocolate cosmos is sometimes listed as a drought tolerant plant. Hardiness: USDA Zones 7 - 10. Chocolate cosmos in hardy down to about 10 °F (-12°C). In climates with colder winters, the tubers must be dug in fall and stored in barely moist peat until planting out the following spring. In zone 7 the tubers should be mulched well for overwintering. Young tubers are less cold hardy than older ones. Propagation: Chocolate cosmos is represented by a single clone that is not self-fertile and therefore does not produce viable seeds. The only way to propagate it is vegetatively, and this can be accomplished by dividing the tubers or rooting basal cuttings of the stem.
Chocolate cosmos grows well in containers. Here it shares a pot with English lavendar and garden verbena.
The flowers of this perennial have the color and smell of chocolate, although some liken the smell to vanilla. Chocolate cosmos is long flowering, usually blooming all summer and well into the fall. Great in borders and mixed flower beds, chocolate cosmos makes a fine cutting flower as well. Deadhead spent flowerheads to prolong blooming and provide support as the plants can get leggy and are prone to falling over. Grow chocolate cosmos in the foreground so its fragrance can be appreciated. Chocolate cosmos is great for container planting, especially where winters are too cold to leave in the ground.
Every individual of Cosmos atrosanguineus in cultivation today comes from the same plant that was collected in Mexico and introduced to the gardening world in 1902. The species has gone extinct in the wild. If it weren’t for gardeners, chocolate cosmos would be listed with the dodo and passenger pigeon.
Among the two dozen or so species of Cosmos, most are annuals and only a couple are perennials. C. diversifolius is a perennial with pink or lavender ray flowers and yellow disk flowers.